The field of the disclosure relates generally to high voltage direct current (HVDC) transmission and distribution (T&D) systems and, more particularly, to systems and methods of operation thereof.
At least some of known electric power generation facilities are physically positioned in a remote geographic region or in an area where physical access is difficult. One example includes power generation facilities geographically located in rugged and/or remote terrain, for example, mountainous hillsides, extended distances from the customers, and off-shore, e.g., off-shore wind turbine installations. More specifically, these wind turbines may be physically nested together in a common geographic region to form a wind turbine farm and are electrically coupled to a common alternating current (AC) collector system. Many of these known wind turbine farms include a separated power conversion assembly, or system, electrically coupled to the AC collector system. Such known separated power conversion assemblies include a rectifier portion that converts the AC generated by the power generation facilities to direct current (DC) and an inverter portion that converts the DC to AC of a predetermined frequency and voltage amplitude. The rectifier portion of the separated power conversion assembly is positioned in close vicinity of the associated power generation facilities and the inverter portion of the separated full power conversion assembly is positioned in a remote facility, such as a land-based facility. Such rectifier and inverter portions are typically electrically connected via submerged HVDC electric power cables that at least partially define an HVDC T&D system. Also, at least some known HVDC T&D systems are coupled to DC loads that do not required an inverter portion of AC conversion.
Many known HVDC T&D systems include mechanical isolation devices, e.g., circuit breakers and reclosers, positioned to define isolatable portions of the system. Such mechanical isolation devices may be opened to isolate electrical faults and, possibly, closed to restore as much of the system to service as possible once the fault is isolated. In addition, many known HVDC T&D systems include a Supervisory Control and Data Acquisition (SCADA) system, or some equivalent, that includes current and voltage sensors positioned therein to facilitate isolation and restoration operations. However, in contrast to AC T&D systems, due to the nature of DC, i.e., no zero-crossing of the amplitudes of DC voltages and currents as a function of time, such opening of the mechanical isolation devices requires opening the devices under load, thereby increasing the risk of arcing at the contactor portions of the mechanical isolation devices with a potential decrease of service life of the contactor portions. Also, in the event of an upward DC current excursion, it is generally considered that an operator has approximately five milliseconds (ms) to isolate the associated fault to avoid a potential decrease of service life of the components in the current path.